Marginal basins through geological time

1981 ◽  
Vol 301 (1461) ◽  
pp. 217-232 ◽  
Keyword(s):  
Plate Tectonics ◽  
Chemical Nature ◽  
Seafloor Spreading ◽  
Continental Margins ◽  
Geological Time ◽  
Volcanic Arcs ◽  
The Past ◽  
Geological Features ◽  
Basin Floor ◽  
Back Arc

Marginal basins are common features of present-day plate tectonics. Whereas some may represent trapped segments of normal ocean floor, many owe their origin to extensional seafloor spreading behind active volcanic arcs. They exhibit a variety of forms. Some are completely intraoceanic; others develop at continental margins, where back-arc spreading may lead to the detachment and dispersal of continental fragments. Marginal basins can be recognized in the early stages of formation; others have developed through more than one pulse of back-arc extension, and some have aborted shortly after formation. Closure of marginal basins may result in preservation of part of the basin floor as obducted ophiolite. Although the reasons why seafloor spreading occurs behind volcanic arcs are still imperfectly understood, all suggested mechanisms invoke a strong link with subduction. Thus if subduction occurred in the past it is logical to expect that fossil marginal basins may be preserved in the geological record. However, allowing for the gradually evolving thermal and chemical nature of the Earth’s mantle, ancient marginal basins need not necessarily duplicate every feature of modern ones. This contribution examines possible Phanerozoic, Proterozoic and Archaean marginal basin analogues in the light of the geological features shown by modern basins and attempts to assess their importance for crustal development.

Tonalites in crustal evolution

1981 ◽  
Vol 301 (1461) ◽  
pp. 293-303 ◽  
Keyword(s):  
Partial Melting ◽  
Plate Tectonics ◽  
Mafic Magma ◽  
Wall Rock ◽  
Continental Margins ◽  
Geological Time ◽  
Roof Rocks ◽  
Basaltic Crust ◽  
Dominant Part ◽  
Mantle Magma

Tonalites, including trondhjemite as a variety, played three roles through geological time in the generation of Earth’s crust. Before about 2.9 Ga ago they were produced largely by simple partial melting of metabasalt to give the dominant part of Archaean grey gneiss terranes. These terranes are notably bimodal; andesitic rocks are rare. Tonalites played a crucial role in the generation of this protocontinental and oldest crust 3.7- 2.9 Ga ago in that they were the only low-density, high-SiO 2 rocks produced directly from basaltic crust. In the enormous event giving the greenstone-granite terranes, mostly 2.8-2.6 Ga ago, tonalites formed in lesser but still important proportions by partial melting of metabasalt in the lower regions of down-buckled greenstone belts and by remobilization of older grey gneisses. Tectonism in the Archaean (3.9- 2.5 Ga ago) perhaps was controlled by small-cell convection (McKenzie & Weiss 1975). Little or no ophiolite or eclogite formed, and only minor andesite. Plate tectonics of modern type (involving large, rigid plates) commenced in the early Proterozoic. Uniformitarianism thus goes back one-half of the age of the earth. Tonalites compose about 5-10 % of crust generated in Proterozoic and Phanerozoic time at convergent oceanic-continental margins. They occur here as minor to prominent members of the compositionally continuous continental-margin batholiths. A simple model of generation of these batholiths is offered: mantle-derived mafic magma pools in the lower crust above a subduction zone reacts with and incorporates wall-rock components (Bowen 1922), and breaches its roof rocks as an initial diapir. This mantle magma also develops a gradient of partial melting in its wall rocks. This wall-rock melt accretes in the collapsed chamber and moves up the conduit broached by the initial diapir, the higher, less siliceous fractions of melting first, the lower, more siliceous (and further removed) fractions of melting last. The process gives in the optimum case a mafic-to-siliceous sequence of diorite or quartz diorite through tonalite or quartz monzodiorite to granodiorite and granite. The model implies that great masses of cumulate phases and refractory wall rock form the roots of continentalmargin batholiths, and that migmatites overlie that residuum and underlie the batholiths.

Plate Tectonics and Macrogeomorphology

2021 ◽  
pp. M58-2021-12
Author(s):  
Michael A. Summerfield
Keyword(s):  
Plate Tectonics ◽  
Earth Science ◽  
Significant Advance ◽  
Continental Margins ◽  
Geological Time ◽  
Landscape Development ◽  
The Earth ◽  
The Status ◽  
Technical Innovations ◽  
Global Tectonics

AbstractThe plate tectonics revolution was the most significant advance in our understanding of the Earth in the 20th century, but initially it had little impact on the discipline of geomorphology. Topography and landscape development were not considered to be important phenomena that deserved attention from the broader earth-science community in the context of the new model of global tectonics. This situation began to change from the 1980s as various technical innovations enabled landscape evolution to be modelled numerically at the regional to sub-continental scales relevant to plate tectonics, and rates of denudation to be quantified over geological time scales. These developments prompted interest amongst earth scientists from fields such as geophysics, geochemistry and geochronology in understanding the evolution of topography, the role of denudation in influencing patterns of crustal deformation, and the interactions between tectonics and surface processes. This trend was well established by the end of the century, and has become even more significant up to the present. In this chapter I review these developments and illustrate how plate tectonics has been related to landscape development, especially in the context of collisional orogens and passive continental margins. I also demonstrate how technical innovations have been pivotal to the expanding interest in macroscale landscape development in the era of plate tectonics, and to the significant enhancement of the status of the discipline of geomorphology in the earth sciences over recent decades.

scholarly journals The fossil record of whip spiders: the past of Amblypygi

PalZ ◽  
2021 ◽  
Author(s):  
Carolin Haug ◽  
Joachim T. Haug
Keyword(s):  
Fossil Record ◽  
3D Imaging ◽  
Three Dimensional ◽  
Dorsal Shield ◽  
Stereo Images ◽  
Geological Time ◽  
High Quality ◽  
The Past ◽  
Over Time

AbstractWhip spiders (Amblypygi), as their name suggests, resemble spiders (Araneae) in some aspects, but differ from them by their heart-shaped (prosomal) dorsal shield, their prominent grasping pedipalps, and their subsequent elongate pair of feeler appendages. The oldest possible occurrences of whip spiders, represented by cuticle fragments, date back to the Devonian (c. 385 mya), but (almost) complete fossils are known from the Carboniferous (c. 300 mya) onwards. The fossils include specimens preserved on slabs or in nodules (Carboniferous, Cretaceous) as well as specimens preserved in amber (Cretaceous, Eocene, Miocene). We review here all fossil whip spider specimens, figure most of them as interpretative drawings or with high-quality photographs including 3D imaging (stereo images) to make the three-dimensional relief of the specimens visible. Furthermore, we amend the list by two new specimens (resulting in 37 in total). The fossil specimens as well as modern whip spiders were measured to analyse possible changes in morphology over time. In general, the shield appears to have become relatively broader and the pedipalps and walking appendages have become more elongate over geological time. The morphological details are discussed in an evolutionary framework and in comparison with results from earlier studies.

scholarly journals Study yields surprises about seafloor spreading in back-arc basins

Eos ◽  
1996 ◽  
Vol 77 (38) ◽  
pp. 365 ◽  
Author(s):  
Etienne Ruellan ◽  
Yves Lagabrielle ◽  
Manabu Tanahashi ◽  
Keyword(s):  
Seafloor Spreading ◽  
Back Arc

scholarly journals Geological archive of the onset of plate tectonics

2018 ◽  
Vol 376 (2132) ◽  
pp. 20170405 ◽  
Author(s):  
Peter A. Cawood ◽  
Chris J. Hawkesworth ◽  
Sergei A. Pisarevsky ◽  
Bruno Dhuime ◽  
Fabio A. Capitanio ◽  
...  
Keyword(s):  
Plate Tectonics ◽  
Foreland Basin ◽  
Sea Floor ◽  
Palaeomagnetic Data ◽  
Peraluminous Granites ◽  
Lithospheric Plates ◽  
Crustal Reworking ◽  
Sea Floor Spreading ◽  
Back Arc ◽  
Earth Dynamics

Plate tectonics, involving a globally linked system of lateral motion of rigid surface plates, is a characteristic feature of our planet, but estimates of how long it has been the modus operandi of lithospheric formation and interactions range from the Hadean to the Neoproterozoic. In this paper, we review sedimentary, igneous and metamorphic proxies along with palaeomagnetic data to infer both the development of rigid lithospheric plates and their independent relative motion, and conclude that significant changes in Earth behaviour occurred in the mid- to late Archaean, between 3.2 Ga and 2.5 Ga. These data include: sedimentary rock associations inferred to have accumulated in passive continental margin settings, marking the onset of sea-floor spreading; the oldest foreland basin deposits associated with lithospheric convergence; a change from thin, new continental crust of mafic composition to thicker crust of intermediate composition, increased crustal reworking and the emplacement of potassic and peraluminous granites, indicating stabilization of the lithosphere; replacement of dome and keel structures in granite-greenstone terranes, which relate to vertical tectonics, by linear thrust imbricated belts; the commencement of temporally paired systems of intermediate and high dT/dP gradients, with the former interpreted to represent subduction to collisional settings and the latter representing possible hinterland back-arc settings or ocean plateau environments. Palaeomagnetic data from the Kaapvaal and Pilbara cratons for the interval 2780–2710 Ma and from the Superior, Kaapvaal and Kola-Karelia cratons for 2700–2440 Ma suggest significant relative movements. We consider these changes in the behaviour and character of the lithosphere to be consistent with a gestational transition from a non-plate tectonic mode, arguably with localized subduction, to the onset of sustained plate tectonics. This article is part of a discussion meeting issue ‘Earth dynamics and the development of plate tectonics'.

Plume-induced subduction and plate fracturation, deep mantle overturn, and the onset of plate tectonics.

2021 ◽  
Author(s):  
Anne Davaille
Keyword(s):  
Plate Tectonics ◽  
Colloidal Dispersions ◽  
Small Scale ◽  
Dense Layer ◽  
Mantle Dynamics ◽  
Simultaneous Generation ◽  
Tensile Fractures ◽  
Back Arc ◽  
The Impact ◽  
Surface Plate

<p>Mantle dynamics can now be recovered in the laboratory, when aqueous colloidal dispersions are dryed from above, and either insulated or heated from below. As their rheology varies from viscous to visco-elasto-plastic to brittle when drying proceeds, a skin (i.e. an experimental lithosphere) develops at the surface. Submitted to buckling, small-scale convection, or an impinging hot plume, this skin can break and one-sided subduction is then observed to proceed. In the case of plume-induced subduction (PIS), the impact of the plume under the skin induces tensile fractures, plume material upwelling through them and spreading at the surface, analogous to volcanic flooding, leading to skin bending and eventually one-sided subduction along arcuate segments which retreat away from the plume. A system of accreting ridges can develop inside the back-arc basin. If PIS develops isolated in an overall stagnant lithosphere, subduction eventually either stops as the result of subducted plate necking, or when plume spreading stops. On the other hand, if the lithosphere contains other heterogeneities (damage) such as faults, accretion ridges or another PIS event, the weight of the subducting plate can induce faraway plate breaking and horizontal mobilization of the surface plate.</p><p>As the lithosphere has to accumulate damage to fracture, it takes time from the first subduction event to the organization of a network of subducting and accreting plates. But the presence of several hot plumes simultaneously accelerates the establishment of an organized pattern of plates, subduction and accretion. And when we run experiments where the mantle contains initially a denser layer at the bottom, the global overturn of this dense layer results in the simultaneous generation of plumes over the whole mantle surface, which produces a burst of PIS events and the quick establishment of a plate tectonic-like regime. <br>Such a global overturn has been proposed to explain the big peak in continental crust growth 2.7 Ga on Earth. Our experiments suggest that it could also have triggered the formation of the plates boundaries and flow organization necessary to plate tectonics.</p>

Origin and Geomorphology

2006 ◽  
Author(s):  
Thomas S. Bianchi
Keyword(s):  
Sea Level ◽  
Rate Of Change ◽  
Interglacial Period ◽  
Continental Margins ◽  
Before Present ◽  
Sea Level Changes ◽  
The Past ◽  
Constant Rate ◽  
Geologic Record ◽  
The U.S

Geologically speaking, estuaries are ephemeral features of the coasts. Upon formation, most begin to fill in with sediments and, in the absence of sea level changes, would have life spans of only a few thousand to tens of thousands of years (Emery and Uchupi, 1972; Schubel, 1972; Schubel and Hirschberg, 1978). Estuaries have been part of the geologic record for at least the past 200 million years (My) BP (before present; Williams, 1960; Clauzon, 1973). However, modern estuaries are recent features that only formed over the past 5000 to 6000 years during the stable interglacial period of the middle to late Holocene epoch (0–10,000 y BP), which followed an extensive rise in sea level at the end of the Pleistocene epoch (1.8 My to 10,000 y BP; Nichols and Biggs, 1985). There is general agreement that four major glaciation to interglacial periods occurred during the Pleistocene. It has been suggested that sea level was reduced from a maximum of about 80 m above sea level during the Aftoninan interglacial to 100 m below sea level during the Wisconsin, some 15,000 to 18,000 y BP (figure 2.1; Fairbridge, 1961). This lowest sea level phase is referred to as low stand and is usually determined by uncovering the oldest drowned shorelines along continental margins (Davis, 1985, 1996); conversely, the highest sea level phase is referred to as high stand. It is generally accepted that low-stand depth is between 130 and 150 m below present sea level and that sea level rose at a fairly constant rate until about 6000 to 7000 y BP (Belknap and Kraft, 1977). A sea level rise of approximately 10 mm y−1 during this period resulted in many coastal plains being inundated with water and a displacement of the shoreline. The phenomenon of rising (transgression) and falling (regression) sea level over time is referred to as eustacy (Suess, 1906). When examining a simplified sea level curve, we find that the rate of change during the Holocene is fairly representative of the Gulf of Mexico and much of the U.S. Atlantic coastline (Curray, 1965).

Multiple dichotomies of the Anthropocene

2016 ◽  
Vol 3 (3) ◽  
pp. 218-230 ◽  
Author(s):  
Whitney J Autin
Keyword(s):  
Popular Culture ◽  
Human Interaction ◽  
Modern Literature ◽  
Formal Definition ◽  
Earth System ◽  
Geological Time ◽  
The Past ◽  
The Earth ◽  
Definition Of ◽  
System Benefit

Anthropocene has developed a varied set of connotations among scientific and non-scientific advocates. As a result, multiple dichotomies of the Anthropocene exist within various scholarly disciplines. The Anthropocene allows people to reinforce and perpetuate preferred views about the implications of human interaction with the Earth System as our management of the environment is called into question. Scientific dichotomies arise from opinions about the need for formal or informal definition and the recognition of a modern versus historical onset of the Anthropocene. Philosophical dichotomies center around good versus dystopian outcomes of Anthropocene and whether or not humanity is part of what historically has been called nature. Political dichotomies insert Anthropocene into classic conservative versus liberal arguments. Artistic dichotomies tend to evaluate the effects of technology on modernism by embracing a nostalgia for the past or projecting an apocalyptic future. Multiple dichotomies drive conversation towards confusion as individuals argue preferred versions of an Anthropocene concept. Philosophical and political perspectives are affecting scientific views of proposed geological time markers for the start of the Anthropocene as conceptual ideologies appear to compete with tangible stratigraphic attributes. Formal definition of the Anthropocene has potential to inhibit popular usage and further confuse an already confused media. Informal stratigraphic usage by scientists and an open-ended view among non-scientific proponents may be the best approach to formulate a robust Anthropocene message. Both humanity and the Earth System benefit from a dynamic tag line that enhances environmental awareness and provides opportunity to modify our habits of resource overuse and ecosystem neglect. Concepts and imagery offered in the form of modern literature and art have the greatest prospect of affecting popular culture perspectives of the Anthropocene’s role in environmental debate.

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